[AVP-ergic mechanism in the rostral ventrolateral medulla:a possible role in stress-induced hyperviscosity]

The study was undertaken to find whether microinjection of vasopressin (AVP) into the rostral ventrolateral medulla (rVLM) affects blood pressure (BP) and blood viscosity in rats and to analyze the effects of AVP-ergic mechanism in the rVLM on stress-induced hyperviscosity of rats. The results are as follows. (1) Microinjection of AVP into the rostral ventrolateral medulla (rVLM) of normal rats resulted in a significant increase in BP and plasma viscosity, which was blocked by bilateral microinjection of AVP V(1) receptor antagonist (d(CH2)5 Tyr(Me)(2) AVP) into the same area. (2) The stress-induced pressor response and hyperviscosity was abolished by microinjection of AVP V(1) receptor antagonist into the rVLM, but not by AVP V(2) receptor antagonist ( adamantaneacetyl(1),O-Et-D-Tyr(2),Val(4),aminobutyryl(6),Arg(8,9) -vasopressin). Microinjection of AVP V(1) receptor antagonist of the same dosage into bilateral caudal ventrolateral medulla (cVLM) or intravenous injection of the antagonist of the same dosage had no effect. The above results suggest that the increase of BP and plasma viscosity induced by microinjection of AVP into rVLM and the stress-induced pressor response and hyperviscosity caused by restraining may be mediated by activation of the AVP V(1) receptor in the rVLM.